The P1 features a 3.8-litre twin-turbo V8 petrol engine. The twin turbos boost the petrol engine at 1.4 bar to deliver 727 bhp (737 PS; 542 kW) and 531 lb⋅ft (720 N⋅m) of torque at 7,500 rpm, combined with an in-house-developed electric motor producing 176 bhp (178 PS; 131 kW) and 192 lb⋅ft (260 N⋅m). With both engine and the electric motor, the P1 has a total power and torque output of 903 bhp (916 PS; 673 kW) and 723 lb⋅ft (980 N⋅m) of torque. The electric motor can be deployed manually by the driver or left in automatic mode, whereby the car's ECUs 'torque fill' the gaps in the petrol engine's output, which is considered turbo lag. This gives the powertrain an effective powerband of almost 7,000 rpm. The car is rear-wheel-drive with a seven-speed dual-clutch gearbox developed by Graziano.
 
Power for the electric motor is stored in a 324-cell lithium-ion high-density battery pack located behind the cabin, developed by Johnson Matthey Battery Systems. The battery can be charged by the engine or through a plug-in equipment and can be fully charged in two hours. The car can be operated using either the petrol engine, the electric motor or with a combination of the two. The P1 has an all-electric range of at least 10 km (6.2 mi) on the combined European drive cycle. Under the EPA cycle, the range in EV mode is 19 mi (31 km). During EV mode the P1 has a petrol consumption of 4.8g/100 mile, and as a result, EPA's all-electric range is rated as zero. The total range is 330 mi (530 km). The P1 combined fuel economy in EV mode was rated by the EPA at 18 MPGe (13 L petrol equivalent/100 km; 22 mpg-imp petrol equivalent), with an energy consumption of 25 kW-hrs/100 mi and petrol consumption of 4.8 gal-US/100 mi. The combined fuel economy when running only with petrol is 17 mpg‑US (14 L/100 km; 20 mpg‑imp), 16 mpg‑US (15 L/100 km; 19 mpg‑imp) for city driving, and 20 mpg‑US (12 L/100 km; 24 mpg‑imp) in highway.
 
The P1 has Formula 1 derived features such as the Instant Power Assist System (IPAS), which gives an instant boost in acceleration via the electric motor, a Drag Reduction System (DRS) which operates the car's rear wing, thereby increasing straight line speed, and a KERS. Both of these features (IPAS, DRS) are operated via two buttons on the steering wheel. It also generates a downforce of 600 kg at 160 mph[13] and it boasts of drag coefficient of only 0.34.
According to McLaren the P1 accelerates from 0–62 mph (0–100 km/h) in 2.8 seconds, 0–200 km/h (0–124 mph) in 6.8 seconds, and 0–300 km/h (0–186 mph) in 16.5 seconds, making it a full 5.5 seconds faster than the F1, and a standing quarter mile is claimed in 9.8 seconds at 152 mph (245 km/h).Autocar tested 0–60 mph (0–97 km/h) mph in 2.8 seconds, 0–120 mph (0–193 km/h) mph in 6.9 seconds, and the standing mile in 18.2 seconds at 178.5 mph (287 km/h). The P1 is electronically limited to a top speed of 217 mph (350 km/h). The P1 has a dry weight of 1,395 kg (3,075 lb), giving it a power-to-weight ratio of 647 bhp/tonne. It has a kerb weight of 1,547 kg (3,411 lb) which translates to 593 bhp/ tonne. Actual kerb weight (full tank of fuel, no luggage or people) of US-spec vehicles is 3411 lb. The P1 also features bespoke Pirelli P-Zero Corsa tyres and specially developed carbon-ceramic brakes from Akebono. According to McLaren it takes 6.2 seconds to brake from 186 mph (300 km/h) to standstill, during which it will cover 246 metres. From 97 km/h (60 mph), it will cover 30.2 metres.